Conventionally, there is a chair provided with a lumbar support apparatus which effectively supports a lumbar portion of a sitting person. Moreover, there is a lumbar support apparatus having a structure which can be fitted with a physique of a sitting person by moving upward and downward a lumbar support member for supporting a lumbar portion (Patent Literature 1). In this lumbar support apparatus, a lumbar portion of a sitting person is supported by a lumbar support main body disposed at the center of a backrest by a support belt which is bridged so as to cross a backrest frame. The support belt is provided at its both ends protrusions which are fitted into holes formed in left and right vertical frame portions of the backrest frame. The lumbar support main body and the support belt supporting the same can be moved in upward and downward directions by shifting the positions of the holes, into which the protrusions are fitted, in the upward and downward directions. The both ends of the support belt supporting the lumbar support main body are sandwiched from their front and rear sides by a cover material and a back frame, and an upward and downward slide structure having a simple structure is formed by the protrusions and the holes between the support belt and the back frame.
Moreover, there is proposed a lumbar support apparatus supporting a lumbar portion by a lumbar support member which is separated into left and right parts (Patent Literature 2). This lumbar support apparatus has a lumbar plate supporting a lumbar vertebra of a sitting person, and the lumbar plate is preliminary divided into two pieces, i.e., a right half plate and a left half plate. Both plates are independently and elastically supported on a support shaft which is rotatably installed on a seat back frame via left and right support arms configured by torsion springs. The left and right support arms configured by the torsion springs are supported by the support shaft, and each of the plates is rotatably disposed on a free end thereof which is bent in a L-shape toward an inside of the back frame. Both ends of the support shaft are fixedly provided with lock plates on which proximal ends of the left and right support arms are locked. By swinging one of the lock plates by a cam which is rotated by an operation knob, the support shaft is rotated so that a restoring force is applied toward a seat direction of the seat back via the torsion spring to each of the lumbar plates at the free ends of the support arm.